There have conventionally been known space transverse single-mode and multi-mode semiconductor laser elements. In single-mode semiconductor laser elements of the two types, the oscillation mode in a waveguide region is restricted to only a single mode to cause the waveguide region to be narrowed. However, the narrower the waveguide region, the smaller the area of the emitting end decreases. Also, an excessive laser beam density at the emitting end has an impact on, for example, the reliability of the semiconductor laser element. Therefore, single-mode semiconductor laser elements are suitable for applications that utilize relatively low-powered laser beams. It is noted that as an example of a single-mode semiconductor laser element, there can be cited, for example, a semiconductor laser device disclosed in Patent Document 1. The semiconductor laser device is a single-mode semiconductor laser and is designed to increase the intensity of laser beams by widening the waveguide region thereof.
On the other hand, in multi-mode semiconductor laser elements, multiple modes may be mixed in a waveguide region to allow the waveguide region to be widened. Therefore, the area of the emitting end can be increased, and laser beams with a relatively high intensity can be emitted. Such multi-mode semiconductor laser elements are suitable for applications that require relatively high-powered laser beams.
However, multi-mode semiconductor laser elements suffer from the following problem. That is, since multiple modes are mixed in a waveguide region, the emitted pattern of laser beams emitted from the emitting end is distorted to result in having a relatively large emitting angle. Therefore, the lens for collecting or collimating such laser beams has a complex shape, resulting in a possibility that no desired laser beam may be obtained and/or production cost may be increased (the lens may be expensive).
As a technique for solving the above-described problems with multi-mode semiconductor laser elements, there can be cited, for example, a resonator disclosed in Patent Document 2. FIG. 1 shows the structure of a conventional resonator, where the area (a) of FIG. 1 is a plan view showing the configuration of the resonator. The resonator 100 has two regions 102a and 102b in an active layer 101. Also, The area (b) of FIG. 1 shows a refractive index distribution at the cross-sections III-III and IV-IV in the area (a) of FIG. 1. As shown in the area (b) of FIG. 1, the refractive index n2 in the regions 102a and 102b is smaller than the refractive index n1 in the other regions in the active layer 101. Also, the regions 102a and 102b are formed in the active layer 101 at an angle where light L reflected perpendicularly at the emitting and reflecting ends 100a and 100b is totally reflected at the side surfaces of the regions 102a and 102b. Patent Document 2 employs such a configuration to limit the optical path of light L resonating in the active layer 101 and thereby to achieve a single-mode oscillation without restricting the width of the waveguide region.
It is noted that as a known technique related to the present invention other than Patent Documents 1 and 2, there is known a semiconductor laser described in Patent Document 3.
Patent Document 1: Japanese Patent Application Laid-Open No. 10-41582
Patent Document 2: International Patent Publication No. WO00/48277
Patent Document 3: Japanese Patent No. 2531719